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Version: v1.10


Expr is a stack based virtual machine. It compiles expressions to bytecode and runs it.

Compilation is done in a few steps:

  • Parse expression to AST
  • Type check AST
    • Apply operator overloading
    • Apply custom AST patching
  • Optimize AST
  • Compile AST to a bytecode

Compiler has a bunch of optimization which will produce a more optimal program.

In array

value in ['foo', 'bar', 'baz']

If Expr finds an in or not in expression with an array, it will be transformed into:

value in {"foo": true, "bar": true, "baz": true}

Constant folding

Arithmetic expressions with constants is computed on compile step and replaced with the result.

-(2 - 5) ** 3 - 2 / (+4 - 3) + -2

Will be compiled to just single number:


In range

user.Age in 18.

Will be replaced with a binary operator:

18 <= user.Age && user.Age <= 32

Const range


Ranges computed on compile stage, replaced with precreated slices.

Const expr

If some function marked as constant expression with expr.ConstExpr. It will be replaced with result of the call, if all arguments are constants.


Will be replaced with result of fib(42) on the compile step.

ConstExpr Example